nation also of the parallel can hardly err so much as 15 seconds of a degree.
This, and several evenings afterwards, I viewed the comet again with such powers as its diluted light would permit, but could not perceive any sort of nucleus which, had it been a single second in diameter, I think, could not well have escaped me. This circumstance seems to be of some consequence to those who turn their thoughts on the investigation of the nature of comets, especially as I have also formerly made the same remark on one of the comets discovered by Mr. Mechain in 1787, a former one of my sister's in 1786, and one of Mr. Pigott's in 1783, in neither of which any defined, solid nucleus, could be perceived.
I have the honour to remain,
Sir, &c.,
Wm. Herschel.
The third comet was discovered on the 7th January, 1790; the fourth on the 17th April of the same year, during her brother's absence from home. It was announced to Sir Joseph Banks in the following letter:—
I am very unwilling to trouble you with incomplete observations, and for that reason did not acquaint you yesterday with the discovery of a comet. I wrote an account of it to Dr. Maskelyne and Mr. Aubert, in hopes that either of those gentlemen, or my brother, whom I expect every day to return, would have furnished me with the means of pointing it out in a proper manner.
But as perhaps several days might pass before I could
